Megaupload complied extremely quickly with DCMA requests by all reports. The non-compliance cited in the indictment appears to be somewhat of a technicality - at worst, only removing links instead of the file. Are you sure Mediafire complies more zealously than Megaupload did?

I don't understand why you view removing the links and not the content as a technicality and not the crux of the issue. If you're ordered to remove content from your servers and do not do so, it's unsurprising that you aren't really complying with the DMCA.

Removing links isn't the same as removing content.

Re-reading the DMCA yesterday was the first time I realized that it actually does require a service like Dropbox to remove every user's copy of a file upon receiving a notice of infringement even if only one of those copies is not allowed and the rest are entirely legal.

Mediafire also don't give incentives for people to put popular files on their system as far as I can tell.

With most services like MegaUpload/Rapidshare you get paid when people download your files, hence their popularity, its a business for a lot of uploaders.